Magnetic recording media

Abstract

Magnetic recording media comprising a non-magnetic base and one or more magnetic layers consisting of an organic binder matrix containing finely divided magnetic material, the said matrix being obtained by electron beam curing of a mixture of from 60 to 100% by weight of a polyurethane acrylate polymer possessing polymerizable double bonds and from 0 to 40% by weight of an acrylate and/or an acrylate prepolymer and/or an N-vinyl monomer and/or an N-vinyl prepolymer.

We claim: 
     
       1. A magnetic recording medium which comprises a non-magnetic base and one or more magnetic layers consisting of an organic binder matrix containing finely divided magnetic material, the said matrix being obtained by electron beam curing of a mixture of from 60 to 100% by weight of a polyurethane acrylate polymer possessing polymerizable double bonds and from 0 to 40% by weight of an acrylate and/or an acrylate prepolymer and/or an N-vinyl monomer and/or an N-vinyl prepolymer, wherein the polyurethane acrylate polymer is composed of (1) one or more diisocyanates,   (2) one or more oligomeric or polymeric diols,   (3) one or more low molecular weight cyclic diols, and   (4) one or more monohydroxyalkyl acrylates, and the amount of NCO groups of the diisocyanate is from 95 to 105% of the number of equivalents of OH groups of components 2, 3 and 4 and the molar amounts of the OH-containing components are chosen so that the concentration of urethane groups is from 2.4 to 3.9 moles per kg of polyurethane acrylate polymer, with the proviso that the number average molecular weight of the polymer is from 1,800 to 10,000 and the ratio of the weight average to the number average molecular weight is from 2.2 to 3.5.